Caro Gertro, ti voglio far divertire (nel senso buono naturalmente!) inviandoti un saggio di come si discute di elmetti e delle loro capacita' cosi' dette balistiche su altri lidi internazionali
nella fattispecie l'HelmNet americano a cui siamo iscritti sia io che Piesse.E' in inglese, ma vista la tua versatilita' nelle lingue e la tua ammirevole buona volonta' avida di apprendimento da non scoraggiare mai, anche quando spesso (non te la prendere perché te lo dico fraternamente),parti volando per l'infinito con riflessioni tutte plausibili, ma spesso senza risposta o quando c'è con risposte che prevedono la lettura di sei o sette capitoli di libri gia' pubblicati,credo potrai giovartene per colmare (in parte) la tua curiosita':
Mark suggested I put together some thoughts on the charateristics of the various types of steel alloy used in steel helmet production, and their effect on helmet design. i have drawn a lot of the materil from Bashford-Dean, who describes WWI French German and Britsh/US helmets in detail and also where i can find it (mostly Casques du Combat) on they types of steels used in i=other helmets. Commnets and corrections would be welcomed.
The first three combat helmets of the 20th century, the French Mle-15, Adrian British Brodie/Mk.I and German Stahlhelm used three very different types of steel, which in turn influenced their desiggs.
To a great extent, the first steel helmet to appear, the Adrian was based in design and manufacturing methods on helmets already being made for the French cavalry and fire brigades. it was made of "mild steel". According to the article on Iron and Steel in the 1911 Encyclopedia Britannica (which gives a good summary of the state of metallurgical technology of the time) "mild steel" - was not steel at all, but a form of cast iron produced through the Bessemer process which eliminated slag and therefore, unlike regular cast iron, was ductile not brittle. It was called "mild steel" for marketing reasons, as cast iron was regarded as an inferior product. Made in several sections (skull, peaks, crest) the helmet was easy to produce, and indeed was produced in huge numbers- reportedly some 20 million between 1915 and 1919. Most producers seem to have been light metal-working establishments or government work-shops. It was also quite light, and elegant (so soldiers were more inclined to wear it) but it ballistic properties were quite poor (not helped by its multi piece construction), according to Bashford Dean - it was less than half that offered by other steel helmets (which probably means a v50 of not much more than 100 m/s). When stuck it was easily deformed which could aggravate the wound effects.
The British and German helmets were both made of alloy steel. Ordinary steel, trades elasticity for hardness, meaning the surface is less prone to penetration but can more easily shatter. In preindustrial times quality armour was face hardened, the surface was carburized to give it a hard steel surface, but underneath it remained wrought iron - allowing elasticity. Alloying iron with metals such as manganese, or nickle in the correct proportions avoided these trade offs by creating a steel that was boith hard and elastic.
After an initial run of 3,000 mild steel helmets, the British Brodie/Mk.I and its US copy the M1917 was made of Hadfields Steel, a 12% manganese alloy steel which offered both great hardness (and thus resistance to penetration) with a high degree of elasticity (which meant it would deform but not shatter or splinter when struck or even when penetrated - albeit sometimes the deformation could be so great as to be fatal even when the round did not penetrate). Dean estimated that British and US helmets could deflect virtually all shrapnel and splinters while the Adrian was effective only 3/4 of the time. Hadfields steel was a recent invention developed by Sir Robert Hadfield in the first decade of the 20th cnetury. Hadfields steel was pressed cold and did not require heat treatment (heating it would, in fact, destroy its properties), and the Brodie design could be stamped in a single operation. Given this simplicity of production it is not surprising that despite the use of such a hard alloy steel, almost 10 million Hadfields steel helmets of this design were produced in the UK and USA. It should be noted US quality control standards seem to have been higher - one frequently sees rippling in WWI British helmets, but not on US ones, while Dean reports the ballistic properties of British-made helmets were slightly inferior to (and less consistent than) its US analogues.
The problem with Hadfields steel came when producing helmets with a deeper draw or more complex shapes such as the US No.2 and No.5 experimental helmets. Early efforts to press these from Hadfields steel resulted in badly rippled helmets with dangerous thinning in the upper skull. Ford had to develop special dies and a multi-step pressing process, even so, the metal at the top of the helmet was abou6t 25% thinner than at the brim.
One perceived advantage of Hadfields steel was that it is non-magnetic and therefore deemed less likly to deflect compasses. While the rims and lugs on WWI helmets were made of mild steel, in WWII the British and USA made all parts of the steel helmets of non-magnetic steel (the French and Belgians who adopted manganese steel between the wars did not follow this trend).
The German Stahlhelm was made of a nickle or nickle-chrome steel alloy (Dean says silicon was added as well which would make the metal easier to work). According to the 1911 Britannica article nickle-steel was preferred for armoured plate because it combines great hardness with elasticity and ductility. In sum it resists penetrations, and deforms rather than shatters when penetrated. Unlike Hadfields steel, nickle steel was worked hot, while this required more complex equipment and processes (about half a dozen stamping operations to make a Stahlhelm) it did however allow the Germans to produce a much deeper helmet with a protective skirt. In ballistic terms the Stahlhelm was comparable or better than the British/US helmet, although again like British-made helmets that were considerable variances - including the exact steel composition) between makers and batches. in all Germany and Austria made some 8 million helmets during WWI.
Except for civil defence uses, mild steel helmets essentially died out after 1918, and as countries began to produce their own steel helmets thet generally opted either for manganese or nickle steel alloys. According to various sources the following countries used manganese steel;
West Germany - magnetic manganese steel before 1960
Ireland M27 (Vickers tried to replicate the Stahlhelm in Hadfields steel, and could only achieve it by using a thinner gauge)
Netherlands M16 (magnetic manganese steel )
Switzerland M18 (magnetic manganese steel - the M40 used " a different alloy" and the M71 "a specially tempered steel")
The following used nickle or where indicated, nickle-chrome steel
Austria - until the introduction of their manganese steel M1 clone in 195
Denmark - until the managnese steel M1 clone was introduced in 1948
Germany (WWI nickle-chrome, WWII nickle-chrome--molybdenum, nickle-silicon for the M42)
Italy Farina -three layers of chrome-nickle steel (Dean says it was "ballistically disappointing"
M33 nickle steel
Japan M30 nickle-chrome-manganese-molybdenum steel
Norway nickle-chrome steel
Poland nickle-chrome steel
Sweden m/26 nickle-chrome steel
Nickle-manganese and nickle-manganese-chrome alloys were also used in some cases:
East Germany M 56 nickle-manganese steel
West Germany Helm1A1 nickle-chrome-manganese steel
Netherlands M22 Röchling (Nickle-chrome manganese) steel
Spain Modelo 26 sin ala Röchling steel
Sweden m/21 nickle-manganese steel
I have found no information on the composition of Soviet helmets, US evaluation of WWII helmets note they were very hard but also very brittle, which might indicate a high carbon steel with little alloy. Post war Soviet helmets have comparable hardness (Rockwell 78 compared to the M1s hardness of 45) to the East German M56 and like east German helmet has superior ballistic to the German Helm1A1 which in turn is somnewhat superior to the US M1 with a resinated fabric liner, albeit of softer steel
A 1950s US evaluation of the Swedish m/37 says it is made of a medium hardness manganese- vanadium steel with a Rockwell hardness of 29-30 and a v50 of 1300 f/s (390 m/s).
Come vedi, il Modello Z spagnolo, neanche e' preso in considerazione.
A seguire, le valutazioni feet /second percentuali di penetrazione sui vari metalli adoperati sugli elmetti moderni.La cosa puo' sembrare noiosa, ma noi sappiamo caro Gertro che sviscerando un argomento a fondo, possiamo saperne di piu'. PaoloM